Tag Archives: arctic sea ice

Arctic sea ice falls below 4 million square kilometers

Following the new record low recorded on August 26, Arctic sea ice extent continued to drop and is now below 4.00 million square kilometers (1.54 million square miles). Compared to September conditions in the 1980s and 1990s, this represents a 45% reduction in the area of the Arctic covered by sea ice. At least one more week likely remains in the melt season.

Overview of conditions

Figure 1. Arctic sea ice extent for August 2012 was 4.72 million square kilometers (1.82 million square miles). The magenta line shows the 1979 to 2000 median extent for that month. The black cross indicates the geographic North Pole. Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
High-resolution image

Throughout the month of August, Arctic sea ice extent tracked below levels observed in 2007, leading to a new record low for the month of 4.72 million square kilometers (1.82 million square miles), as assessed over the period of satellite observations,1979 to present. Extent was unusually low for all sectors of the Arctic, except the East Greenland Sea where the ice edge remained near its normal position. On August 26, the 5-day running average for ice extent dropped below the previous record low daily extent, observed on September 18, 2007, of 4.17 million square kilometers (1.61 million square miles). By the end of the month, daily extent had dropped below 4.00 million square kilometers (1.54 million square miles). Typically, the melt season ends around the second week in September. 

Conditions in context

Figure 2. The graph above shows Arctic sea ice extent as of September 3, 2012, along with daily ice extent data for the previous five years. 2012 is shown in blue, 2011 in orange, 2010 in pink, 2009 in navy, 2008 in purple, and 2007 in green. The 1979 to 2000 average is in dark gray. The gray area around this average line shows the two standard deviation range of the data. Sea Ice Index data.

Credit: National Snow and Ice Data Center
High-resolution image

In 2012, the rate of ice loss for August was 91,700 square kilometers (35,400 square miles) per day, the fastest observed for the month of August over the period of satellite observations. In August 2007, ice was lost at a rate of 66,000 square kilometers (25,400 square miles) per day, and in 2008, the year with the previous highest August ice loss, the rate was 80,600 square kilometers (31,100 square miles) per day. The average ice loss for August is 55,100 square kilometers (21,300 square miles) per day. This rapid pace of ice loss in 2012 was dominated by large losses in the East Siberian and the Chukchi seas, likely caused in part by the strong cyclone that entered the region earlier in the month and helped to break up the ice. However, even after the cyclone had dissipated, ice loss continued at a rate of 77,800 square kilometers (30,000 square miles) per day.

August air temperatures at the 925 hPa level (approximately 3,000 feet above the surface) remained slightly above average (1 to 3 degrees Celsius, or 2 to 5 degrees Fahrenheit) over the much of the Pacific sector of the Arctic Ocean as well as at its central sector, with slightly higher temperatures in the Beaufort Sea (approximately 4 degrees Celsius, or 7 degrees Fahrenheit above average). On the Atlantic side, the Kara and Barents seas continued to have air temperatures around 1 to 4 degrees Celsius (2 to 7 degrees Fahrenheit) below average.

At the end of August, ice remained in the Western Parry Channel, and neither the northern or southern routes of the Northwest Passage were open. While much of the ice has cleared out, ice still remains, as confirmed by our colleague Steve Howell at the Canadian Ice Service. In the latter half of August, more ice actually moved into the passage routes when ice was pushed down into the channels from the north. Whether that ice will clear out remains to be seen.

August 2012 compared to previous years

Figure 3. Monthly August ice extent for 1979 to 2012 shows a decline of 10.2% per decade.


Credit: National Snow and Ice Data Center
High-resolution image

The monthly averaged ice extent for August was 4.72 million square kilometers (1.82 square miles). This is 2.94 million square kilometers (1.14 million square miles) below the 1979 to 2000 average extent, and 640,000 square kilometers (247,000 square miles) below the previous record low for August set in 2007. Including 2012, the August trend is -78,100 square kilometers (-30,200 square miles) per year, or -10.2 % per decade relative to the 1979 to 2000 average.

Evolution of sea surface temperatures in August

sea surface temperature images

Figure 4. A buoy deployed on August 8, 2012 in open water during the storm initially shows a very warm 10-meter (33-foot) thick surface mixed layer (upper left image). On August 12 (upper right image), the buoy enters a relatively cooler patch, gradually warms, enters another cool patch 12 days later (bottom left image), and then starts to warm again through August 26 (bottom right image). Red, orange, and yellow indicate higher temperatures, while blues and purples indicate lower temperatures.

Credit: University of Washington Polar Science Center
High-resolution image

In recent summers, Arctic Ocean sea surface temperatures (SSTs) have been anomalously high (see our 2010 and 2011 end-of-summer posts), in part linked to loss of the reflective ice cover that allows darker open water areas to readily absorb solar radiation and warm the mixed layer of the ocean. According to Mike Steele, Wendy Ermold and Ignatius Rigor of the University of Washington, SSTs in the Beaufort, Chukchi, and Laptev seas were once again anomalously high before the strong cyclone (mentioned earlier and discussed in our previous post) entered the East Siberian and Chukchi seas on August 5, 2012. SSTs were as much as 5 degrees Celsius (9 degrees Fahrenheit) above normal along the coastal areas in those seas. After the storm, the warm water that developed through summer was interspersed with large areas of cold water created by ice melt. By the third week of August, sea surface temperatures were mostly back to levels observed before the storm, but with a few more patches of colder water interspersed from additional ice melt.

A closer view of the variation in SSTs before and after the storm is recorded in the University of Washington Polar Science Center UpTempO buoy data. A buoy deployed on August 8, 2012 in open water during the storm initially shows a very warm 10-meter (33-foot) thick surface mixed layer, likely the result of solar heating. On August 12, the buoy enters a relatively cooler patch, gradually warms, enters another cool patch 12 days later and then starts to warm again through August 26. These patches of cooler water may be a result of ice melt and/or the impact of advection from the storm.

Old ice continues to decline

Figure 5. These images from March 2012 (left) and August 2012 (right) show the age of the ice cover in spring and at the end of summer. Much of the Arctic ice cover now consists of first-year ice (shown in purple), which tends to melt rapidly in summer’s warmth. However, the oldest ice, that had survived five or more summers (shown in white), declined by 51%.

Credit: M. Tschudi and J. Maslanik, University of Colorado Boulder
High-resolution image

Ice age is an important indicator of the health of the ice cover. Old ice, also called multiyear ice, tends to be thicker ice and less prone to melting out in summer. The last few summers have seen increased losses of multiyear ice in the Pacific sector of the Arctic; multiyear ice that is transported into the Beaufort and Chukchi seas tends to melt out in summer before being transported back to the central Arctic Ocean through the clockwise Beaufort Gyre circulation. This summer, the tongue of multiyear ice along the Alaska coast mostly melted out by the end of August, with a small remnant left in the Chukchi Sea. The ice on the Pacific side of the Arctic has melted back to the edge of the multiyear ice cover, which should help to slow further ice loss in the region. In the Laptev Sea, by contrast, a large amount of first-year ice remains. In the last two weeks, open water areas have developed within the first-year ice in the Laptev Sea, helping to further foster melt in that region.

Between mid-March and the third week of August, the total amount of multiyear ice within the Arctic Ocean declined by 33%, and the oldest ice, ice older than five years, declined by 51%.

Further reading

Kwok, R., and G. F. Cunningham. 2010. Contribution of melt in the Beaufort Sea to the decline in Arctic multiyear sea ice coverage: 1993–2009. Geophys. Res. Lett., 37, L20501, doi:10.1029/2010GL044678.

Maslanik, J.A., C. Fowler, J. Stroeve, and W. Emery. 2011. Distribution and trends in Arctic sea ice age through spring 2011. Geophys. Res. Lett., 38, L13502, doi:10.1029/2011GL047735.

Arctic sea ice extent breaks 2007 record low

Arctic sea ice appears to have broken the 2007 record daily extent and is now the lowest in the satellite era. With two to three more weeks left in the melt season, sea ice continues to track below 2007 daily extents.

Please note that this is not an announcement of the sea ice minimum extent for 2012. NSIDC will release numbers for the 2012 daily minimum extent when it occurs. A full analysis of the melt season will be published in early October, once monthly data are available for September.

Overview of conditions

Figure 1. Arctic sea ice extent for August 26, 2012 (right) was 4.10 million square kilometers (1.58 million square miles), which was 70,000 square kilometers (27,000 square miles) below the September 18, 2007 daily extent of 4.17 million square kilometers (1.61 million square miles, left). The orange line shows the 1979 to 2000 median extent for that day. The black cross indicates the geographic North Pole. Sea Ice Index data. About the data.


Credit: National Snow and Ice Data Center
High-resolution images: Figure 1a , Figure 1b

Arctic sea ice extent fell to 4.10 million square kilometers (1.58 million square miles) on August 26, 2012. This was 70,000 square kilometers (27,000 square miles) below the September 18, 2007 daily extent of 4.17 million square kilometers (1.61 million square miles).

Including this year, the six lowest ice extents in the satellite record have occurred in the last six years (2007 to 2012).

Conditions in context

Figure 2. The graph above shows Arctic sea ice extent as of August 26, 2012, along with daily ice extent data for 2007, the previous record low year, and 1980, the record high year. 2012 is shown in blue, 2007 in green, and 1980 in orange. The 1979 to 2000 average is in dark gray. The gray area around this average line shows the two standard deviation range of the data. The 1981 to 2010 average is in sky blue. Sea Ice Index data.

Credit: National Snow and Ice Data Center
High-resolution image  

 

 

After tracking near 2007 levels through July, the extent declined rapidly in early August. Since then, the loss rate has slowed some, averaging about 75,000 square kilometers (29,000 square miles) per day—equivalent to the size of the state of South Carolina. However, this is still much faster than the normal rate at this time of year of about 40,000 square kilometers per day (15,000 square miles).

Note that the date and extent of the 2007 minimum have changed since we originally posted in 2007; see our Frequently Asked Questions for more information.

 

 

 

 

 

 

A summer storm in the Arctic

Arctic sea ice extent during the first two weeks of August continued to track below 2007 record low daily ice extents. As of August 13, ice extent was already among the four lowest summer minimum extents in the satellite record, with about five weeks still remaining in the melt season. Sea ice extent dropped rapidly between August 4 and August 8. While this drop coincided with an intense storm over the central Arctic Ocean, it is unclear if the storm prompted the rapid ice loss. Overall, weather patterns in the Arctic Ocean through the summer of 2012 have been a mixed bag, with no consistent pattern.

Overview of conditions

Figure 1. Arctic sea ice extent for August 13, 2012 was 5.09 million square kilometers (1.97 million square miles), 483,000 square kilometers (186,000 square miles) below the same day in 2007. The orange line shows the 1979 to 2000 median extent for that day. The black cross indicates the geographic North Pole. Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
High-resolution image

Arctic sea ice extent on August 13 was 5.09 million square kilometers (1.97 million square miles). This is 2.69 million square kilometers (1.04 million square miles) below the 1979 to 2000 average extent for the date, and is 483,000 square kilometers (186,000 square miles) below the previous record low for the date, which occurred in 2007. ( Note: The sea ice extent originally published on August 14, 2012 was the actual one-day value for August 13. We normally report the five-day trailing mean, so to be consistent we have updated the post with these numbers instead of the one-day value. See the Sea Ice Index Documentation for more information about the five-day trailing mean.) Low extent for the Arctic as a whole is driven by extensive open water on the Atlantic side of the Arctic, the Beaufort Sea, and—due to rapid ice loss over the past two weeks—the East Siberian Sea. Ice is near its normal (1979 to 2000) extent only off the northeastern Greenland coast. Ice near the coast in eastern Siberia continues to block sections of the Northern Sea Route. The western entrance to the Northwest Passage via McClure Strait remains blocked.

Conditions in context

Figure 2. The graph above shows Arctic sea ice extent as of August 13, 2012, along with daily ice extent data for the previous five years. 2012 is shown in blue, 2011 in orange, 2010 in pink, 2009 in navy, 2008 in purple, and 2007 in green. The gray area around the average line shows the two standard deviation range of the data. Sea Ice Index data.

Credit: National Snow and Ice Data Center
High-resolution image

The average pace of ice loss since late June has been rapid at just over 100,000 square kilometers (38,000 square miles) per day. However, this pace nearly doubled for a few days in early August during a major Arctic cyclonic storm, discussed below. Unlike the summer of 2007 when a persistent pattern of high pressure was present over the central Arctic Ocean and a pattern of low pressure was over the northern Eurasian coast, the summer of 2012 has been characterized by variable conditions. Air tempertures at the 925 hPa level (about 3000 feet above the ocean surface) of 1 to 3 degrees Celsius (1.8 to 5.4 degrees Fahrenheit) above the 1981 to 2012 average have been the rule from central Greenland, northern Canada, and Alaska northward into the central Arctic Ocean. Cooler than average conditions (1 to 2 degrees Celsius or 1.8 to 3.6 degrees Fahrenheit) were observed in a small region of eastern Siberia extending into the East Siberian Sea, helping explain the persistence of low concentration ice in this region through early August.

The Great Arctic Cyclone of 2012

Figure 3. This subsection of the surface weather analysis from the Canadian Meteorological Centre for August 6, 2012 (at 0600 Greenwich Mean Time) shows a very strong cyclone over the central Arctic Ocean north of Alaska. The isobars (lines of equal pressure) are very tightly packed around the low pressure system, indicating strong winds. Greenland is on the right side of the figure while Canada is at the bottom.

Credit: Canadian Meteorological Centre
High-resolution image

A low pressure system entered the Arctic Ocean from the eastern Siberian coast on August 4 and then strengthened rapidly over the central Arctic Ocean. On August 6 the central pressure of the cyclone reached 964 hPa, an extremely low value for this region. It persisted over the central Arctic Ocean over the next several days, and slowly dissipated. The storm initially brought warm and very windy conditions to the Chukchi and East Siberian seas (August 5), but low temperatures prevailed later.

Figure 4. These maps of sea ice concentration from the Special Sensor Microwave Imager/Sounder (SSMIS) passive microwave sensor highlight the very rapid loss of ice in the western Arctic (northwest of Alaska) during the strong Arctic storm. Magenta and purple colors indicate ice concentration near 100%; yellow, green, and pale blue indicate 60% to 20% ice concentration.

Credit: National Snow and Ice Data Center courtesy IUP Bremen
High-resolution image

Low pressure systems over the Arctic Ocean tend to cause the ice to diverge or spread out and cover a larger area. These storms often bring cool conditions and even snowfall. In contrast, high pressure systems over the Arctic cause the sea ice to converge. Summers dominated by low pressure systems over the central Arctic Ocean tend to end up with greater ice extent than summers dominated by high pressure systems.

However, the effects of an individual strong storm, like that observed in early August, can be complex. While much of the region influenced by the August cyclone experienced a sudden drop in temperature, areas influenced by winds from the south experienced a rise in temperature. Coincident with the storm, a large area of low concentration ice in the East Siberian Sea (concentrations typically below 50%) rapidly melted out. On three consecutive days (August 7, 8, and 9), sea ice extent dropped by nearly 200,000 square kilometers (77,220 square miles). This could be due to mechanical break up of the ice and increased melting by strong winds and wave action during the storm. However, it may be simply a coincidence of timing, given that the low concentration ice in the region was already poised to rapidly melt out.

Further Reading

Long, Z. and W. Perrie. 2012. Air-sea interactions during an Arctic storm. Journal of Geophysical Research, 117, D15103, doi:10.1029/2011JD016985.

Screen, J. A., I. Simmonds, and K. Keay. 2011. Dramatic interannual changes of perennial Arctic sea ice linked to abnormal summer storm activity. Journal of Geophysical Research, 116, D15105, doi:10.1029/2011JD015847.

Serreze, M. C. and A. P. Barrett. 2008. The summer cyclone maximum over the central Arctic Ocean. Journal of Climate, 21, doi:10.1175/2007JCLI1810.1.

A most interesting Arctic summer

Arctic sea ice extent declined quickly in July, continuing the pattern seen in June. On August 1, ice extent was just below levels recorded for the same date in 2007, the year that saw the record minimum ice extent in September. Low sea ice concentrations are present over large parts of the western Arctic Ocean. Warm conditions dominated the weather for most of the Arctic Ocean and surrounding lands. For a brief period in early July, nearly all of the Greenland ice sheet experienced surface melt, a rare event.

Overview of conditions

Sea ice image for July 2012

Figure 1. Arctic sea ice extent for July 2012 was 7.94 million square kilometers (3.07 million square miles). The magenta line shows the 1979 to 2000 median extent for that month. The black cross indicates the geographic North Pole. Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
High-resolution image

Arctic sea ice extent for July 2012 averaged 7.94 million square kilometers (3.07 million square miles). This was 2.12 million square kilometers (819,000 square miles) below the 1979 to 2000 average extent. July 2012 ice extent was 20,000 square kilometers (7,700 square miles) above the 2011 record July low.

As throughout the summer, the low ice extent for the Arctic as a whole is primarily due to extensive open water on the Atlantic side of the Arctic (Kara, Laptev and East Siberian seas) and the Beaufort Sea. By August 1, open water in the Laptev Sea, along the Siberian coast, had reached nearly 80oN latitude. Ice extent remains near average in the Chukchi Sea, and ice continues to block sections of the both the Northern Sea Route and the Northwest Passage. The ice extent recorded for August 1 of 6.53 million square kilometers (2.52 million square kilometers) is the lowest in the satellite record. The previous record for the same date was set in 2007 at 6.64 million square kilometers (2.56 million square miles), when the current record low September ice extent was set.

Conditions in context

Figure 2. The graph above shows Arctic sea ice extent as of August 5, 2012, along with daily ice extent data for the 2011 and for 2007, the record low year. 2012 is shown in blue, 2011 in orange, and 2007 in green. The gray area around the average line shows the two standard deviation range of the data. Sea Ice Index data.

Credit: National Snow and Ice Data Center
High-resolution image

In July, the Arctic lost a total of 2.97 million square kilometers (1.15 million square miles) of ice. The largest July total loss, 3.53 million square kilometers (1.36 million square miles) occurred in the year 2007. Warm conditions prevailed over most of the Arctic Ocean; temperatures at the 925 hPa level (about 3,000 feet above the ocean surface) were typically 1 to 3 degrees Celsius (1.8 to 5.4 degrees Fahrenheit) above the 1981 to 2010 average over the Beaufort Sea and regions to the north, as well as over Baffin Bay. By contrast, temperatures were 1 to 3 degrees Celsius below average over the Norwegian Sea. Weather patterns over the Arctic Ocean varied substantially through the month, as they have done throughout the melt season.

July 2012 compared to recent years

Graph of sea ice extent trend

Figure 3. Monthly July ice extent for 1979 to 2012 shows a decline of 7.1% per decade.

Credit: National Snow and Ice Data Center
High-resolution image

Arctic sea ice extent for July 2012 was the second lowest in the satellite record, behind 2011. Through 2012, the linear rate of decline for July Arctic ice extent over the satellite record is 7.1% per decade.

MODIS data shows low concentration ice

MODIS image of sea ice

Figure 4. This image from the Moderate Resolution Imaging Spectroradiometer (MODIS), taken in late July, shows areas of low concentration sea ice in the Beaufort Sea, north of Alaska. Barrow, Alaska is at the top left. The resolution is 500 meters. The cloud band covering much of the lower right part of the image is associated with an approaching storm.

Credit: NASA Goddard Space Flight Center, Rapid Response
High-resolution image

In our last post (July 24, 2012) we commented on large areas of low ice concentration depicted in Special Sensor Microwave Imager/Sounder (SSMIS) data in the Beaufort and Chukchi seas, the Canadian Archipelago, the East Greenland Sea, and north of Siberia. These areas of low ice concentration ice can be seen clearly in visible-band data collected by the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard NASA’s Aqua and Terra satellites.

The MODIS image shows polygonal floes of multi-year ice, as well as thin, gray first-year ice, and dark open water in the Beaufort Sea, north of Alaska. Most of these areas of low concentration ice will likely melt over the next month. Because MODIS senses light reflected from the surface as opposed to the emission of microwave radiation, its ability to see the surface depends on cloud cover.

Comparisons between observed and modeled September sea ice trends

Graph of sea ice model results

Figure 5. This figure shows the observed September sea ice extent for 1952 to 2011 (bold black line) and extents for 1900 to 2100 from the CMIP3 models using the “business as usual” SRESA1B greenhouse gas emissions scenario (the blue line averaging results from all of the model runs with the blue shading showing the +/- 1 standard deviation of the different model runs) and from the CMIP5 archive, using the RCP 4.5 scenario (pink line and pink shading). The darker pink shading shows where the simulations from CMIP3 and CMIP5 overlap each other.

Credit: National Snow and Ice Data Center courtesy Stroeve et al. 2012
High-resolution image

Previous research at NSIDC documented that September Arctic ice extent has declined faster than models predicted it would. The comparison was between observations and simulated trends from models participating in the World Climate Research Programme Coupled Model Intercomparison Project Phase 3 (CMIP3). These climate models were used in the 2007 4th Assessment report of the Intergovernmental Panel on Climate Change (IPCC). In a new paper, Stroeve et al. (2012) compared the observed 1979-2011 September trend for the Arctic against trends over the same period from the next generation of models in the CMIP5 archive. While the newer CMIP5 models do a better job of simulating the observed trend, most of the modeled ice extent trends are still smaller than the observed downward trend. NSIDC is working with researchers to further improve the models, which help extend and refine our understanding of the climate system.

Extensive melt over the Greenland Ice Sheet

Figure 6. This figure shows the daily, cumulative area of the Greenland ice sheet showing surface melt for 2012, 2011, 2010 and for the 1980 to 1999 mean. While melt was unusually extensive through May and June of 2012, the melt area increased rapidly in early July in response to an unusually warm weather event.

Credit: National Snow and Ice Data Center courtesy Marco Tedesco, CUNY
High-resolution image

This summer, the ocean has not been the only place where unusual melt has been observed in the Arctic. NASA researchers reported that for several days in early July, nearly the entire Greenland ice sheet experienced a brief period of surface melt, including at the summit of the ice sheet. Typically, about half of the ice sheet sees some surface melting during summer, but this tends to be confined to the lower elevations. The 2012 event was associated with a high-pressure weather pattern bringing unusually warm temperatures over the higher elevations of the ice sheet. While the event has not been seen previously in the 34-year satellite record, there is evidence in ice core data from Summit, Greenland of similar events occurring several times over the past few thousand years. These melt events recorded in the ice cores from Summit show an overall average frequency of about once every 150 years since the end of the last ice age. Perhaps more important, however, is the extraordinary high melting occurring this year around the lower elevations in Greenland. Figure 6 shows that the first few months of melt exceeded past higher-than-average melt seasons. Flooding and damage to structures has been reported in some areas where this melt runs off the ice sheet and fills streams and rivers along the Greenland coast. The surface melt runoff, as well as the flow of ice and the resulting calving of icebergs, are contributors to sea level rise. Along with the substantial summer sea ice extent decline and the early Northern Hemisphere snow melt, the pace of Greenland surface melt suggests that 2012 is yet another interesting summer in the Arctic.

For more information and images, visit Greenland Melting.

References

Stroeve, J. C., V. Kattsov, A. P. Barrett, M. C. Serreze, T. Pavlova, M. M. Holland, and W. N. Meier. 2012. Trends in Arctic sea ice extent from CMIP5, CMIP3 and observations. Geophys. Res. Lett., doi:10.1029/2012GL052676, in press.

Sea ice continues to track at low levels

Arctic sea ice continued to track at levels far below average through the middle of July, with open water in the Kara and Barents seas reaching as far north as typically seen during September. Melt onset began earlier than normal throughout most of the Arctic.

Figure 1. Arctic sea ice extent for July 23, 2012 was 7.32 million square kilometers (2.82 million square miles). The orange line shows the 1979 to 2000 median extent for that day. The black cross indicates the geographic North Pole. Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
High-resolution image

Overview of conditions
As of July 23, 2012, sea ice extent was 7.32 million square kilometers (2.82 million square miles). On the same day last year, ice extent was 7.22 million square kilometers (2.78 million square miles), the record low for this day.

Arctic sea ice extent continued to track at very low levels, setting daily record lows for the satellite era for a few days in early July. Extent is especially low in the Barents, Kara, and Laptev seas. In the Barents and Kara seas, the area of open water extends to the north coasts of Franz Josef Land and Severnaya Zemlya, as far north as typically seen during September, the end of the summer melt season. Polynyas in the Beaufort and East Siberian seas continued to expand during the first half of July. By sharp contrast, ice extent in the Chukchi Sea remains near normal levels. In this region the ice has retreated back to the edge of the multiyear ice cover. Ice cover in the East Greenland Sea, while of generally low concentration, remains slightly more extensive than normal.

Figure 2. The graph above shows Arctic sea ice extent as of July 23, 2012, along with daily ice extent data for the previous five years. 2012 is shown in blue, 2011 in orange, 2010 in pink, 2009 in navy, 2008 in purple, and 2007 in green. The gray area around the average line shows the two standard deviation range of the data. Sea Ice Index data.

Credit: National Snow and Ice Data Center
High-resolution image

Conditions in context
The first part of July was once again dominated by high sea level pressure over the Beaufort Sea, combined with low sea level pressure over Siberia and Alaska. As discussed in last month’s post, this pressure pattern tends to promote above-average temperatures and enhances ice transport out of the Arctic through Fram Strait. Beginning July 11th, the pressure pattern changed as cyclones moved into the central Arctic Ocean, bringing in cooler temperatures and helping to slow ice loss. Air temperatures at the 925 hPa level (about 3000 feet) in the central Arctic and the Beaufort Sea were 1 to 4 degrees Celsius (2 to 7 degrees Fahrenheit) above normal as averaged from July 1 to July 14. In the Beaufort and Chukchi seas, the sea ice has retreated to the edge of the multiyear ice cover. As a result of the anomalously high air temperatures, melt over the multiyear ice cover is extensive and ice concentrations are low. Anomalously low air temperatures for that period were found in the Barents, Kara, and East Greenland seas (1 to 3 degrees Celsius, or 2 to 6 degrees Fahrenheit, below the 1981 to 2010 climatology).

Early melt onset
The timing of seasonal melt onset, which can be estimated from satellite passive microwave data, plays an important role in the amount of ice that melts each summer. Unusually early melt onset means an early reduction in the surface albedo, allowing for more solar heating of the ice, which in turn allows melt ponds and open water areas to develop earlier in the melt season. In 2012, melt began earlier than normal (as compared to averages for the period 1979 to 2000) throughout most of the Arctic, the exceptions being the Bering Sea and the East Greenland Sea. Melt in the Kara and Barents seas began more than two weeks earlier than normal. Melt onset for the Laptev Sea region as a whole started on June 1 and was the earliest seen in the satellite record. Melt began 12 and 9 days earlier than normal averaged over the Beaufort and Chukchi seas, respectively.

Figure 4. This composite image from the SSMIS instrument obtained on July 23, 2012 shows areas of low ice concentration in the Beaufort and Chukchi seas, the Canadian Archipelago, the East Greenland Sea, and north of Siberia. Purple indicates areas of high sea ice concentration, while yellow and red indicate lower ice concentration. Blue shows open water and green shows land.

Credit: National Snow and Ice Data Center courtesy IUP Bremen
High-resolution image

Low ice concentrations
NSIDC uses satellite data from the Special Sensor Microwave Imager (SSM/I) and the Special Sensor Microwave Imager/Sounder (SSMIS) instruments, in part because they provide the longest consistent time series of data. However, more recent sensors such as the Advanced Microwave Scanning Radiometer-Earth Observing System (AMSR-E) provide a more detailed perspective. In particular, we can examine ice concentration, which tells us how much ice is in a pixel, providing information on how vulnerable the ice may be to summer melting.

In October 2011, the AMSR-E instrument on board the NASA Aqua satellite ceased operation, dealing a blow to the science community. This is because its higher spatial resolution and advanced technology provided detailed ice information to complement the long-term record of the Special Sensor Microwave Imager/Sounder (SSMIS) instrument. However, the Japanese Aerospace Exploration Agency (JAXA) successfully launched a new satellite called Shizuku, or Global Change Observation Mission 1st-Water (GCOM-W1), on May 18, 2012. The Shizuku carries a new Advanced Microwave Scanning Radiometer (AMSR2) instrument, a sensor similar to AMSR-E. As soon as calibration and validation of AMSR2 are complete, the University of Bremen will once again produce maps of sea ice concentration at a fairly high resolution (about 6 kilometers).

In the meantime, the University of Bremen offers sea ice concentration maps from the lower-resolution SSMIS. The July 23 chart shows areas of low sea ice concentration in the Beaufort and Chukchi seas, the Canadian Archipelago, the East Greenland Sea, and north of Siberia. In the Beaufort and Chukchi seas, low ice concentrations and polynyas are found over areas of multiyear sea ice, where open water areas have developed between individual multiyear ice floes and significant ponding on the ice is observed. Low ice concentrations mean a low surface albedo, allowing for more of the sun’s energy to be absorbed, melting even more sea ice. This makes the multiyear ice in the Beaufort and Chukchi seas vulnerable to melting out this summer.

Rapid sea ice retreat in June

Arctic sea ice extent declined quickly in June, setting record daily lows for a brief period in the middle of the month. Strong ice loss in the Kara, Bering, and Beaufort seas, and Hudson and Baffin bays, led the overall retreat. Northern Hemisphere snow extent was unusually low in May and June, continuing a pattern of rapid spring snow melt seen in the past six years.

sea ice extent

Figure 1. Arctic sea ice extent for June 2012 was 10.97 million square kilometers (4.24 million square miles). The magenta line shows the 1979 to 2000 median extent for that month. The black cross indicates the geographic North Pole. Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
High-resolution image
Daily data files

Overview of conditions
Arctic sea ice extent for June 2012 averaged 10.97 million square kilometers (4.24 million square miles). This was 1.18 million square kilometers (456,000 square miles) below the 1979 to 2000 average extent. The last three Junes (2010-2012) are the three lowest in the satellite record. June 2012 ice extent was 140,000 square kilometers (54,000 square miles) above the 2010 record low. Ice losses were notable in the Kara Sea, and in the Beaufort Sea, where a large polynya has formed. Retreat of ice in the Hudson and Baffin bays also contributed to the low June 2012 extent. The only area of the Arctic where sea ice extent is currently above average is along the eastern Greenland coast.

The ice extent recorded for 30 June 2012 of 9.59 million square kilometers (3.70 million square miles) would not normally be expected until July 21, based on 1979-2000 averages. This puts extent decline three weeks ahead of schedule.

graph of sea ice extents

Figure 2. The graph above shows Arctic sea ice extent as of July 2, 2012, along with daily ice extent data for the previous five years. 2012 is shown in blue, 2011 in orange, 2010 in pink, 2009 in navy, 2008 in purple, and 2007 in green. The gray area around the average line shows the two standard deviation range of the data. Sea Ice Index data.

Credit: National Snow and Ice Data Center
High-resolution image
Daily data files

Conditions in context
In June, the Arctic lost a total of 2.86 million square kilometers (1.10 million square miles) of ice. This is the largest June ice loss in the satellite record. Similar to May, the month was characterized by a period of especially rapid ice loss (discussed in the mid-month entry, June 19th) followed by a period of slower loss. Warm conditions prevailed over most of the Arctic; temperatures at the 925 hPa level (about 3000 feet above the ocean surface) were typically 1 to 4 degrees Celsius (1.8 to 7.2 degrees Fahrenheit) above the 1981 to 2010 average, and as much as 7 to 9 degrees Celsius (12.6 to 16.2 degrees Fahrenheit) above average over northern Eurasia and near southern Baffin Bay. Weather patterns over the Arctic Ocean varied substantially through the month.

Figure 3. Monthly June ice extent for 1979 to 2012 shows a decline of 3.7% per decade.

Credit: National Snow and Ice Data Center
High-resolution image

June 2012 compared to recent years
Arctic sea ice extent for June 2012 was well below average for the month compared to the satellite record from 1979 to 2000. It was the second lowest in the satellite record, behind 2010. Through 2012, the linear rate of decline for June Arctic ice extent over the satellite record is 3.7% per decade.

ice conditions in the field

Figure 4. These photographs show sea ice on the fast ice near Barrow, Alaska. (a) Chris Polashenski stands in a melt pond with instrumentation, (b) honeycombed sample of rotten ice taken from the bottom of a melt pond, (c) sea ice rubble field after winds pushed the weakened sea ice onto the shore.

Credit: National Snow and Ice Data Center, courtesy Chris Polanshenski of CRREL as part of the SIZONET project.
High-resolution image

A report from the field
Dr. Chris Polashenski of the Cold Regions Research Lab (CRREL) recently returned from making sea ice measurements on landfast ice a few kilometers offshore near Barrow, Alaska as part of the National Science Foundation and NASA funded Seasonal Ice Zone Observing Network (SIZONET) project. He and his fellow researchers made some interesting observations. Prior to the onset of melt, the ice was thicker than observed in recent years – around 1.8 meters (5.9 feet) as compared to typical conditions of around 1.4 meters (4.6 feet). Despite this thick ice at the beginning of the season, melt proceeded relatively rapidly. Melt ponds began forming on June 4—a typical timing for recent years, but high temperatures, sunny afternoons, and foggy nights combined to speed the melt of ice thereafter.

On June 17-18, a confluence of weather conditions, including a daytime high of 19 degrees Celsius (66 degrees Fahrenheit), overnight condensing fog, and bright sun in the afternoon combined to produce exceptional surface melt of just under 11 centimeters (4.3 inches) in a 24-hour period, according to preliminary lidar data. By June 18, ice conditions had deteriorated significantly and with strong winds forecast out of the west, safety dictated it was time to get off the ice. Collisions of the pack with the weakened shore fast ice on June 21-23 resulted in substantial deformation and a series of ice pushes onto the beach, an amazing process to watch from the safety of land.

Such field observations may only be representative of the local area. However, they provide context for basin-wide observations and a better understanding of local processes.

map of snow cover anomaliesmap of snow cover anomalies

Figure 5. June 2012 set a record low for Northern Hemisphere snow cover extent. Figure 5 (a) graphs snow extent for Junes from 1967 to 2012. Figure 5 (b) maps snow cover anomalies in the Northern Hemisphere.

Credit: National Snow and Ice Data Center courtesy Rutgers University Snow Lab.

High-resolution image: June snow cover anomalies graph
High-resolution image: June snow cover anomalies map

Graph of May snow cover anomalies
Map of May snow cover anomalies

Low June snow extent
Snow cover over Northern Hemisphere lands retreated rapidly in May and June, leaving the Arctic Ocean coastline nearly snow free. June 2012 set a record low for snow extent (for a 45-year period of record spanning 1967-2012) by a significant margin. Snow extent for June 2012 was more than 1 million square kilometers (386,000 square miles) below the previous record set in 2010. Snow extent for 2011 was a close third lowest. May 2012 had third lowest snow extent for the period of record. This rapid and early retreat of snow cover exposes large, darker underlying surfaces to the sun early in the season, fostering higher air temperatures and warmer soils.

A note on the daily sea ice data
NSIDC has published the underlying data used for the Daily Sea Ice Extent image and the Daily Sea Ice Extent 5-Month Time Series graph. Please see the links below for documentation for the Sea Ice Index and links to the data:

Documentation–Daily extent data file

Documentation–Climatology file

Sea ice tracking at record low levels

After a period of rapid ice loss through the first half of June, sea ice extent is now slightly below 2010 levels, the previous record low at this time of year. Sea level pressure patterns have been favorable for the retreat of sea ice for much of the past month.

Figure 1. Arctic sea ice extent for 18 June 2012 (left) was 10.62 million square kilometers (4.10 million square miles), 31,000 square kilometers (12,000 square miles) below the same day in 2010 (right). The orange line shows the 1979 to 2000 median extent for that day. The black cross indicates the geographic North Pole. Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
High-resolution images: Figure 1a, Figure 1b

Overview of conditions

On June 18, the five-day average sea ice extent was 10.62 million square kilometers (4.10 million square miles). This was 31,000 square kilometers (12,000 square miles) below the same day in 2010, the record low for the day and 824,000 square kilometers (318,000 square miles) below the same day in 2007, the year of record low September extent.

Figure 2. The graph above shows Arctic sea ice extent as of June 18, 2012, along with daily ice extent data for the previous five years. 2012 is shown in blue, 2011 in orange, 2010 in pink, 2009 in navy, 2008 in purple, and 2007 in green. The gray area around the average line shows the two standard deviation range of the data. Sea Ice Index data.

Credit: National Snow and Ice Data Center
High-resolution image

Conditions in context

The main contributors to the unusually rapid ice loss to this point in June are the disappearance of most of the winter sea ice in the Bering Sea, rapid ice loss in the Barents and Kara Seas, and early development of open water areas in the Beaufort and Laptev Seas north of Alaska and Siberia. Recent ice loss rates have been 100,000 to 150,000 square kilometers (38,600 to 57,900 square miles) per day, which is more than double the climatological rate.

Figure 3: This map of mean sea level pressure from 15 May 2012 to 15 June 2012 shows a pattern of high pressure over the Beaufort Sea and a pattern of low pressure over the Laptev Sea, conditions favorable to summer ice loss.

Credit: NSIDC courtesy NOAA/ESRL PSD
High-resolution image

Sea level pressure favors the advection of ice

A pattern of high pressure over the Beaufort Sea and low pressure over the Laptev Sea has been present for the past few weeks. This pattern is favorable for summer ice loss, by advecting warm winds from the south (in eastern Asia) to melt the ice and transport it away from the coastlines in Siberia and Alaska. The high pressure over the Beaufort leads to generally clear skies, and temperatures are now above freezing over much of the Arctic pack. Snow cover in the far north is nearly gone, earlier than normal, allowing the coastal land to warm faster.

Early melt onset, and clear skies near the solstice are favorable conditions for more rapid melting, and warming of the ocean in open-water areas. The persistence of this type of pressure pattern throughout summer 2007 was a major factor toward causing the record low September extent that year. Conversely, in 2010, the patterns were not as favorable for loss of ice and the seasonal decline slowed later in the summer, and the extent did not approach the record low levels of 2007.

While these patterns and conditions have looked similar to 2007, over the last couple days the high pressure pattern over the Beaufort Sea has broken down. And while the extent is at a record low for the date, it is still early in the melt season. Changing weather patterns throughout the summer will affect the exact trajectory of the sea ice extent through the rest of the melt season.

Arctic sea ice variable, ends May below average

After reaching near-average levels in late April, sea ice extent declined rapidly during the early part of May. The rest of the month saw a slower rate of decline. Ice extent in the Bering Sea remained above average throughout the month.

Figure 1. Arctic sea ice extent for May 2012 was 13.13 million square kilometers (5.07 million square miles). The magenta line shows the 1979 to 2000 median extent for that month. The black cross indicates the geographic North Pole. Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
High-resolution image

Overview of conditions
Arctic sea ice extent for May 2012 averaged 13.13 million square kilometers (5.07 million square miles). This was 480,000 square kilometers (185,000 square miles) below the 1979 to 2000 average extent. This May’s extent was similar to the May 2008 – 2010 extent, but it was higher than May 2011. May ice extent was 550,000 square kilometers (212,000 square miles) above the record low for the month, which happened in the year 2004.

Ice cover remained extensive in the Bering Sea, continuing the pattern observed this past winter and spring. The anomalously heavy ice conditions were countered by unusually low extents in the Barents and Kara Seas, resulting in Arctic-wide ice conditions that remained below normal. By the end of the month, open water areas had begun to form along some parts of Arctic Ocean coast.

While the ice extent for May is not especially low this year, there is little correlation between the extent of the ice cover in May and that at the end of the melt season in September.

Figure 2. The graph above shows Arctic sea ice extent as of June 4, 2012, along with daily ice extent data for the previous five years. 2012 is shown in blue, 2011 in orange, 2010 in pink, 2009 in navy, 2008 in purple, and 2007 in green. The gray area around the average line shows the two standard deviation range of the data. Sea Ice Index data.

Credit: National Snow and Ice Data Center
High-resolution image

Conditions in context
For May, the Arctic as a whole lost 1.62 million square kilometers (625,000 square miles) of ice, which was 180,000 square kilometers (69,500 square miles) more than the 1979 to 2000 average. The average daily rate of ice loss was 52,000 square kilometers (20,000 square miles) per day, which was slightly faster than the long-term average of 46,000 square kilometers (18,000 square miles) per day. However, the rate of ice loss for the month was composed of two distinct periods: a rapid loss of ice during the first part of the month, followed by near-average rates during the latter part of the month.

Air temperatures for May were higher than usual over the central Arctic Ocean and the Canadian Archipelago. Over the Bering Sea, Hudson Bay, and parts of the East Greenland and Norwegian seas, temperatures were slightly below average.

Figure 3. Monthly May ice extent for 1979 to 2012 shows a decline of 2.3% per decade.

Credit: National Snow and Ice Data Center
High-resolution image

May 2012 compared to past years
Arctic sea ice extent for May 2012 was below average for the month, compared to the satellite record from 1979 to 2000. However, the ice extent this May was not as low as it has been in some recent years. Including the year 2012, the linear rate of decline for May ice extent over the satellite record is 2.3% per decade.

May and April have the smallest trends of the year, indicating that spring is a period during the year when there is less variability and conditions tend to converge. It also demonstrates that spring extents are not necessarily indicative of conditions later in the summer.

Figure 4. This map of sea level pressure anomalies for May 2012 shows that low pressure continued to dominate off of southern Alaska, resulting in northerly winds in the Bering Sea.

Credit: NSIDC courtesy NOAA/ESRL PSD
High-resolution image

A persistent pattern of extensive ice in the Bering Sea

Continuing the pattern of the past six months, ice cover remained unusually extensive in the Bering Sea. Normally by the end of May, the Bering is largely ice-free, but this year, 350,000 square kilometers (135,000 square miles) of ice remained. As was also the case for February through April, May 2012 had the highest average Bering Sea ice extent for the month in the satellite record.

The higher than normal extent and late spring break up of the ice cover in the Bering Sea are mainly due to unusually low air temperatures and persistent winds from the north, related to a region of low atmospheric pressure centered over Kodiak, Alaska. As these cold winds slowed ice melt, they also pushed the ice edge to the south. The heavy ice in the region may delay the start of Shell Alaska’s Arctic drilling this summer, which will be the first exploratory drilling in the Arctic Ocean in 20 years.

With the overall springtime warming of the Arctic, the ice has nevertheless started to break up and large areas of open water are now present in the northern part of the Bering Sea.

Figure 5. In this Moderate Resolution Imaging Spectroradiometer (MODIS) Arctic Mosaic image for the Beaufort Sea on May 29, 2012, open water is apparent between fast ice along the coast and the broken-up floes off-shore. Toward the bottom of the image, thin clouds can be seen over the open water.

Credit: NASA/GSFC, Rapid Response
High-resolution image

Open water areas within the Arctic Ocean

Although ice extent has remained high in the Bering Sea, open water areas have developed in parts of the Arctic Ocean, notably along the coasts of the Beaufort and Laptev seas. These openings are largely driven by winds pushing the ice away from fast ice, ice that is attached to the coast and that does not move with the winds. That the open water areas have not refrozen points to the relatively warm conditions over the Arctic, particularly in the Beaufort Sea.

The ice cover in the southern Beaufort Sea is also substantially broken up, with many individual ice floes instead of a consolidated pack. This makes the ice in this region vulnerable to enhanced melt during summer, as the sun rises higher in the sky and the dark open water areas between the floes readily absorb solar energy.

Quicker thickness data from NASA IceBridge

As we discussed last month, thickness information is extremely important for understanding the state of the ice cover. It is particularly important to seasonal forecasts (such as the SEARCH Sea Ice Outlook that will be released later this month), because thinner ice is more likely to melt completely during summer.

Sea ice age can be inferred from satellite data, and can help indicate the locations of relatively thin versus relatively thick ice. But direct measurements of ice thickness have been limited. Satellite missions such as ICESat and CryoSat, which measure ice thickness with altimeters, have been extremely valuable in better understanding overall changes in Arctic sea ice volume.

Currently, the NASA IceBridge mission supplies both sea ice thickness and snow depth measurements in spring, providing timely information on the state of the ice cover as the melt season begins. IceBridge data are collected from aircraft that fly over the ice cover carrying a suite of instruments, including altimeters that can directly measure ice thickness above the surface. These measurements are at high spatial resolution that can also be used to validate satellite data.

This year, the IceBridge Arctic sea ice campaign collected data in late March and early April, and provided data to NSIDC for distribution shortly thereafter. The data, collected from the North American side of the Arctic, indicate thick ice north of Greenland due to wind and ocean current patterns piling ice into thick ridges. In the Beaufort Sea, the offshore ice is fairly thin (1 to 2 meters, or 3 to 6 feet), indicative of first-year ice. Such thin ice will be prone to melt out completely this summer.

Ice along the Alaskan coast is thicker. Thicker ice tends to have a deeper overlying snow cover. The amount of snow is an important factor in the summer melt, because the snow reflects solar energy. The snow must melt away before surface melting of the ice can begin in earnest.

February ice extent low in the Barents Sea, high in the Bering Sea

As in January, sea ice extent in February was low on the Atlantic side of the Arctic, but unusually high on the Pacific side of the Arctic, remaining lower than average overall. At the end of the month, ice extent rose sharply, as winds changed and started spreading out the ice cover.

Sea ice extent in late winter can go up and down very quickly, getting pushed together or dispersed by strong winds. Ice extent usually reaches its annual maximum sometime in late February or March, but the exact date varies widely from year to year.

Arctic sea ice extent for February 2012 was 14.56 million square kilometers (5.62 million square miles). The magenta line shows the 1979 to 2000 median extent for that month. The black cross indicates the geographic North Pole. Sea Ice Index data.

Credit: National Snow and Ice Data Center
High-resolution image

Overview of conditions
Arctic sea ice extent in February 2012 averaged 14.56 million square kilometers (5.62 million square miles). This is the fifth-lowest February ice extent in the 1979 to 2012 satellite data record, 1.06 million square kilometers (409,000 square miles) below the 1979 to 2000 average extent.

Continuing the pattern established in January, conditions differed greatly between the Atlantic and Pacific sides of the Arctic. On the Atlantic side, especially in the Barents Sea, air temperatures were higher than average and ice extent was unusually low. February ice extent for the Barents Sea was the lowest in the satellite record.  Air temperatures over the Laptev, Kara and Barents seas ranged from 4 to 8 degrees Celsius (7 to 14 degrees Fahrenheit) above average at the 925 hectopascal (hPa ) level (about 3000 feet above sea level).  In contrast, on the Pacific side, February ice extent in the Bering Sea was the second highest in the satellite record, paired with air temperatures that were 3 to 5 degrees Celsius (5 to 9 degrees Fahrenheit) below average at the 925 hPa level.

graph showing years and ice extent

The graph above shows daily Arctic sea ice extent as of March 5, 2012, along with the ice extents for the previous four years. 2011 is shown in light blue, 2010 is in pink, 2009 in dark blue, 2008 is in purple, and 2007, the year with the record low minimum, is dashed green. The gray area around the average line shows the two standard deviation range of the data. Sea Ice Index data.

Credit: National Snow and Ice Data Center
High-resolution image

Conditions in context

Overall, the Arctic gained 956,000 square kilometers (369,000 square miles) of ice during the month. This was 486,000 square kilometers (188,000 square miles) more than the average ice growth for February 1979 to 2000. The overall low ice extent for the month stemmed mostly from the low ice extent in the Barents Sea: the extensive ice in the Bering Sea was not enough to compensate. On average, the Barents Sea has 865,000 square kilometers (334,000 square miles) of ice for the month of February. This year there were only 401,000 square kilometers (155,000 square miles) of ice in that region, the lowest recorded in the satellite data record.

At the end of February, ice extent rose sharply. Data from the NSIDC Multisensor Analyzed Sea Ice Extent (MASIE) showed that the rise came mainly from the Bering Sea and Baffin Bay. In the Bering Sea and Baffin Bay, winds pushed the ice extent southward. Ice growth in the Kara Sea also contributed to the rise in ice extent. In the Kara Sea, westerly winds that had been keeping the area ice-free shifted, allowing the open water areas to freeze over. During late winter, ice extent can change quickly as winds push extensive ice cover together, or spread out ice floes over a greater area.

Monthly February ice extent for 1979 to 2012 shows a decline of 3.0% per decade.

Credit: National Snow and Ice Data Center
High-resolution image

February 2012 compared to past years
Arctic sea ice extent for February 2012 was the fifth lowest in the satellite record. Including the year 2012, the linear rate of decline for February ice extent over the satellite record is 3.0% per decade. Based on the satellite record, through 2003, average February ice extent had never been lower than 15 million square kilometers (5.79 million square miles). February ice extent has not exceeded that mark eight out of the nine years since 2003.

This photograph of sea ice near Greenland was taken on March 18, 2011 from the NASA P3 aircraft. The IceBridge mission is collecting data on ice thickness, an important measure of the health of sea ice.

Credit: NASA/ATM automatic Cambot system
High-resolution image

IceBridge thickness data
Measuring ice thickness is critical to assessing the overall health of Arctic sea ice. The passive microwave data that NSIDC presents here provide only ice extent, a two-dimensional measure of ice cover. But ice can vary in thickness from a few centimeters to several meters, and scientists want to know if the ice pack is thinning overall as well as declining in extent. A new study by NASA scientist Ron Kwok compared ice thickness data collected by airplanes during the ongoing Operation IceBridge with thickness data from the NASA Ice, Cloud and Land Elevation Satellite (ICESat), which ended its mission in 2009. IceBridge is an airborne data-collection mission that started in 2009, in order to bridge the data gap between the first ICESat and ICESat-2, which is scheduled to launch in 2016.

Kwok found good agreement between simultaneous IceBridge and ICESat freeboard measurements made in 2009. Freeboard is the elevation of sea ice above the ocean surface, and provides a measure of ice thickness. These results show that IceBridge measurements will be able to bridge the gap between the ICESat and ICESat-2 satellite missions and add to other ice thickness data from the European Space Association (ESA) Cryosat-2. Satellite measurements of ice thickness provide a third dimension of information on the changing sea ice cover, helping scientists to more accurately assess the amount of sea ice in the Arctic.

Data collected by the IceBridge mission is archived and distributed by the NSIDC IceBridge Data program.

These images show the general effects of the positive phase (left) and negative phase (right) of the NAO. Red dots show the location of harp seal breeding grounds.

Credit: Johnston, et. al., 2012
High-resolution image

Regional ice conditions and harp seals
Many animals rely on sea ice as part of their habitat. Harp seals, for example, give birth to and care for their young on floes of sea ice. Recent research by David Johnston and colleagues at Duke University showed that harp seals in the northwest Atlantic have higher mortality rates during years when the North Atlantic Oscillation (NAO) is in its negative phase, a pattern that favors low ice cover in the Labrador Sea and Gulf of St. Lawrence, where harp seals breed. 

This winter, the NAO has mostly been in a positive phase and ice conditions in the Labrador Sea and Gulf of St. Lawrence have been at near-normal levels. However, in recent years, ice conditions in the region have been very low. The study showed a longer-term decline in sea ice cover of up to 6% per decade across all North Atlantic harp seal breeding grounds since 1979. While harp seals are well-suited to deal with natural short-term shifts in ice conditions, they may not be able to adapt to the combined effects of both short-term variability and long-term climate change.

Further reading
Friedlaender, A.S., D.W. Johnston and P.N. Halpin. 2010. Effects of the North Atlantic Oscillation on sea ice breeding habitats of harp seals (Pagophilus groenlandicus) across the North Atlantic, Progress in Oceanography, 86, 261-266. 

Johnston DW, Bowers MT, Friedlaender AS , Lavigne DM. 2012. The Effects of Climate Change on Harp Seals (Pagophilus groenlandicus). PLoS ONE, 7(1): e29158. doi:10.1371/journal.pone.0029158.

Kwok, R., G.F. Cunningham, S.S. Manizade and W.B. Krabill. 2012. Arctic sea ice freeboard from IceBridge acquisitions in 2009: Estimates and comparisons with ICESat, Journal of Geophysical Research, Vol. 117, C02018, doi:10.1029/2011JC007654.